Some of the emails we've sent are just tests or other special cases, and we don't particularly want them on our dashboard or skewing our performance stats.

Some things can't be tested with the "send to a test group" function, but instead require you to actually send the message. See the case specified in this suggestion:

http://rediscovery.uservoice.com/forums/137015-raiser-s-edge-discovery-topics/suggestions/7868385-preview-online-express-email-based-on-a-constituen